Solder bump measuring method and apparatus

ABSTRACT

A work having a number of solder bumps on a substrate is mounted on a work positioning mechanism, and scanned by an optical micro head to measure errors of a mount posture of the work. Each stage is controlled to correct the errors, and thereafter, the apex positions of the bumps are scanned and measured. The measurement results are collected by a personal computer, and the measurement results together with control data of each axis are sent to a main personal computer and displayed on its screen. An error of an apex position of each bump from a regression plane is calculated, and if the error is smaller than a reference value, the work is judged to be good.

This is a divisional application of U.S. Ser. No. 09/289,386, filed Apr.12, 1999 now U.S. Pat. No. 6,196,441, issued Mar. 6, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for measuringsolder bumps formed on a semiconductor module such as LSI, on TAB (TapeAutomated Bonding), and the like.

2. Description of the Related Art

FIGS. 1A to 1C illustrate the structure of a semiconductor module 1having a number of solder bumps. FIG. 1A is a diagram showing theoverall structure of the semiconductor module. FIG. 1B is an enlargedview of a bump area A of the semiconductor module and illustrates arelative position of solder bumps. FIG. 1C is an enlarged view of a bump10 (corresponding to B in FIG. 1A).

A number of solder bumps 10 are formed on the bottom of thesemiconductor module 1. Each bump is used for connection to a wiringboard on which the semiconductor module 1 is mounted. The semiconductormodule 1 is of a square shape having a side length of, for example, 10mm. Solder bumps 10 are formed on the surface 8 at a pitch of, forexample, 450 μm, totalling in number to 23×23.

Each bump 10 is generally spherical as shown in the enlarged view ofFIG. 1C.

There is no apparatus for automatically measuring a height of a numberof spherical bumps to date. Therefore, height is measured visually byusing a focus-of-depth microscope or the like.

Works (to be measured) such as semiconductor modules formed with anumber of bumps are positioned at a later process on a wiring board, andbumps are heated and melted in a heating furnace to be connected to thewiring board.

In order to reliably connect the bumps, it is necessary to correctlymeasure a height of each bump at its apex.

The size of each bump is required to have predetermined values so thatadjacent bumps and wiring connections are prevented from beingelectrically shorted.

However, it is very difficult to measure heights of a number of bumpscorrectly and in a short time.

One of the inventors of this invention has proposed techniques ofmeasuring a height of a work by using an optical beam, as disclosed inJP-A-2-80905.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method andapparatus capable of measuring bumps on a work correctly at high speed.

The measuring method of this invention comprises the steps of: mountinga work to be measured on a table, the work having solder bump rows;detecting a reference bump from the solder bumps by using a laseroptical micro head; scanning the solder bump rows with the optical microhead and detecting a shift amount of a mount posture of the work;correcting the shift amount of the mount posture of the work by scanningthe table; and measuring height positions of apexes of all the solderbumps with the optical micro head.

The method of the invention further comprises the steps of calculating aregression plane formed by the apexes of the solder bumps andcalculating a relative apex position of each solder bump relative to thecalculated regression plane. The method of the invention furthercomprises the steps of calculating a standard deviation of relativeheights and judging from the standard deviation and the apex height ofeach bump whether the work is defective or not.

A measure apparatus of this invention comprises: a table for placingthereon a work to be measured, the work having solder bump rows; movingmeans for moving the table in a two-dimensional plane in twoperpendicular axis directions; rotating means for rotating the tableabout a vertical axis; inclining means for inclining the table; a laseroptical micro head mounted on the table to be movable in the verticalaxis direction; a personal computer for recording data measured by theoptical micro head in the form of digital data; controlling means forcontrolling the table and the optical micro head; a personal computerfor calculating a height position of an apex of each solder bump inaccordance with the data measured by the optical micro head; a displayscreen for displaying the calculated results; and a printer for printingout the calculated results.

According to the present invention, a work is measured by scanning alight spot by the optical micro head. Therefore, the drive speed can bechanged depending upon a necessary measurement precision and the size ofthe work, so that high speed, high precision, and versatility can berealized for various applications.

As above, the invention provides a method and apparatus for measuringheights of all of a number of bumps formed on a work such as an LSI andjudging whether the work is good or not. The invention is applicable toworks having highly dense bumps expected in the future.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a semiconductor module used as a work to bemeasured, and FIGS. 1B and 1C are enlarged views showing bumps and abump on the semiconductor module.

FIG. 2 is a perspective view of a measuring apparatus of this invention.

FIG. 3 is a block diagram showing the structure of the measuringapparatus of the invention.

FIG. 4 is a perspective view showing the structure of an optical microhead.

FIG. 5 is a plan view illustrating scanning of an optical micro head.

FIG. 6 is a diagram showing an example of measurement results.

FIGS. 7A and 7B are diagrams illustrating a method of measuring the apexof a solder bump on a substrate surface.

FIG. 8 is a diagram illustrating the effects of swell of a substrate.

FIG. 9 is a plan view illustrating a mount of a work on a work table.

FIG. 10 is a plan view illustrating a method of detecting a bump apexposition.

FIG. 11 is a diagram illustrating measurement results with substratemount errors.

FIG. 12A is a diagram illustrating measurement results with substratemount errors, and FIG. 12B is a diagram illustrating rotation correctionof mount errors.

FIG. 13 is a diagram illustrating measurement results with substratemount errors.

FIG. 14 is a diagram illustrating a regression plane of apexes of solderbumps.

FIG. 15 is a graph showing a standard deviation of measurement results.

FIG. 16 is a diagram illustrating a display screen of a monitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a diagram showing an apparatus used with a solder bumpmeasuring method of this invention.

This measuring apparatus generally indicated by reference numeral 100has an operation stage 105 on which a work is placed and measured, acontrol unit 120, an operation panel 130, a printer 140 for outputtingmeasurement results, a monitor TV for monitoring a measurement area ofthe operation stage 105, and the like.

FIG. 3 is a block diagram showing the control system of the measuringapparatus 100 shown in FIG. 2. A table frame on which a work 1 is placedis mounted on an anti-vibration base 210. The table frame has a θ stage212 for controlling an angle around the work vertical axis (Z axis), anX stage 214 for controlling a motion in a guide axis (X axis) in theplane perpendicular to the vertical axis, a Y stage 214 for controllinga motion in a guide axis (Y axis) perpendicular to the X axis, and a βinclination stage 218 and an α inclination stage 220 respectively forcontrolling inclination of the surface of a work positioning mechanism(work table) 230.

Each control axis is controlled by outputs from an axiscontroller/driver apparatus 240.

An optical microsensor 250 is mounted on a Z axis driver mechanism 270and is used for controlling the optical microsensor in the Z axisrelative to the work table 230. This optical microsensor 250 can beretracted away from a measuring position of the work table 230 by aretracting mechanism 272 so that the work 1 can be easily placed on ordismounted from the operation stage. A motion amount in the Z axis ismeasured by a digital micrometer 274.

An optical camera 252 is mounted at the side of the optical microsensor250, and the state of the measuring area can be monitored by a CRT 150.

The optical microsensor 250 is controlled by a controller 260, and themeasured data is A/D converted and supplied via a digital input/outputinterface 264 to a computing apparatus, for example, a personal computer266.

The measurement results are supplied via a digital input/outputinterface 280 to a computing apparatus, for example, a master personalcomputer 110. The measurement results are displayed on the personalcomputer 110 and printed out from a printer 140.

The measurement results of solder bumps are judged in accordance withcoordinate data of each bump position and correction amount data of eachcontrol axis, by using an operation switch 284.

FIG. 4 shows the structure of the optical micro head 250 which has asemiconductor laser 252 and a light receiving element 255. A laser beamradiated from the semiconductor laser 252 passes through a lens 253 andapplied to a bump 10 as a laser beam LB. The laser beam reflected at thesurface of the bump 10 passes through a lens 254 and is received by thelight receiving element 255. The light receiving element 255 measuresthe height position of the bump surface in accordance with a positionwhere the reflected light is received, by using the principle oftriangulation, and also detects the amount of reflected light.

The X axis of the table is aligned with the optical axis of the laserbeam LB.

FIG. 5 shows scan paths along which the bump 10 is scanned with thelaser beam LB. The surface area including the apex of the bump 10 ismeasured by three paths. Three paths are used for obtaining a correctvalue while considering the position displacement of each bump. Threepaths are only illustrative and a plurality of paths may be setdepending upon the measurement conditions.

FIG. 6 shows an example of the measurement results wherein the abscissarepresents the X axis and the ordinate represents a detected level. Afirst curve C1 indicates a level of reflected and received light, and asecond curve C2 indicates a change in height of the bump.

A reference value TL of the level of the reflected and received light C1is preset. An X axis position where the received light becomes largerthan the reference value TL and an X axis position where the receivedlight becomes smaller than the reference value are detected. The valueof the height signal C2 at the middle coordinate position X10 is used asthe height of the apex of the bump.

FIGS. 7A and 7B illustrate a relationship between the surface 8 of thesubstrate 2 and the height position of the bump 10.

The laser beam LB scans the surface 8 of the substrate 2 and the bump 10to detect the height positions of the surface 8 and bump 10.

The substrate is not always absolutely flat, since it may have a swellor the like. Therefore, as shown in FIG. 8, a regression plane P1 of thesurface 8 of the substrate 8 and a regression plane P2 of the apexes ofbumps are calculated.

An absolute height H1 from the regression plane P1 and a relative heightH2 from the regression plane P2 are then obtained.

There is not always a constant relationship between the size and shapeof the substrate of a work to be measured and the position of eachsolder bump on the substrate, because a work precision of the substratehas a limit. Therefore, after the work is placed on the table, the mountposture of the work is aligned before measurement.

The regression plane means a virtual plane which minimizes the distancesto bumps. This is the same concept as a regression line. It is moreeffective from the viewpoint of process to evaluate the bump height fromthe distance to the regression plane than using the absolute bumpheight.

FIG. 9 shows a positioning device for positioning an LSI carrier as awork on the work table 230 which moves in X and Y directions.

A work 1 is of a square shape. A right angle block 232 conformal to thework 1 is mounted on the table 230. The block 232 has reference stoppers233. The work 1 is pushed against the stoppers 233 by a pushing pin 234which moves toward the stoppers 233.

The table 230 has a suction device 235 which uses a negative pressure tosuck the bottom of the work 1.

There are some errors of the outer dimension of the LSI substrate andbump positions because of substrate scribe errors, shrinkage ofsubstrate material, or the like.

For this reason, a process of detecting the position of a first bump10-1 of the work 1 is executed as illustrated in FIG. 10.

The controller knows in advance the position, as designed, of the firstbump 10-1 relative to the substrate of the work 1. Therefore, first, thecoordinates of the X axis of the table are aligned with the designcoordinates of the first bump 10-1, and a first scan S-1 is performedfor measurement while moving the table in the Y direction.

With this scan S-1, a curve indicating a change in the amount ofreflected and received light of the first bump 10-1, such as the curveC1 shown in FIG. 6, can be obtained. The center position of the lightamount of this curve is obtained, this position being assumed as thecenter (origin) of the first bump 10-1. If the received light amountdoes not exceed the reference value, the X axis coordinates are shiftedby a distance D1 to execute a second scan S-2 to detect the temporaryorigin and determine the Y axis coordinates.

Next, after the Y axis coordinates are fixed, a scan S-3 is performed inthe X axis direction to determine the position of the first bump 10-1from the center of the received light amount. If the received lightamount does not exceed the reference value at the X axis coordinates,the Y axis coordinates are shifted by a distance D2 to execute a scanS-4 to perform similar operations as above.

The coordinate values obtained in the above manner are used as atemporary origin K1.

A first row of bumps including the temporary origin K1 is scanned(S-10), and the apex positions of bumps are obtained which show areceived light amount in excess of the reference value. An average valueof shift amounts between the X axis coordinates of apex positions andthe designed X axis coordinates is calculated (refer to FIG. 11).

Next, a similar scan (S-11) is performed for the bump row remotest fromhe above bump row to thereby calculate an average value of shift amountsin the X axis coordinates.

In accordance with shift amounts, a correction value of a distance fromthe end of the work substrate to the first bump in the X axis directionis determined to correct the X axis coordinates of the origin.

Similar scans are executed in the Y axis direction to calculate theshift amounts of the Y axis coordinates and correct the Y axiscoordinates of the origin.

If the work is mounted being rotated about the center axis and a scan isperformed by shifting the scan position by a designed value, then thepeak values of the received light amount on the scan line change in apredetermined direction and a shift occurs between the peak position andthe design position (refer to FIG. 12A).

In accordance with this change, a correction value for the work rotationangle θ is calculated to rotate the θ stage and correct its position(refer to FIG. 12B).

While a scan for the θ correction is executed in the X axis direction,the heights at positions 8-1, 8-2, 8-3, . . . on the work substrate arealso detected (refer to FIG. 8). In accordance with the change in theheights, a regression line L-1 is calculated and a correction value αfor an inclination angle from the reference line (horizontal line) inthe X axis direction is calculated to correct the α inclination stage220.

Similarly, a correction value β for an inclination angle in the Y axisdirection is calculated to correct the β inclination stage 218.

After the above alignment processes are completed, all bumps are scannedto measure the apex heights as already described with FIG. 5.

With precise alignment, a measuring laser beam can be scanned highlyprecisely at high speed. Therefore, the bump heights can be measuredhighly precisely at high speed.

FIG. 14 shows a regression plane PL-1 formed by the measured apexpositions of bumps 10. A shift of each bump apex position is calculatedfrom this regression plane PL-1 and the judgement results are displayedon the display 112.

FIG. 15 is a graph showing the measurement results displayed on thescreen.

The abscissa represents a difference between each bump apex and theregression plane, and the ordinate represents the number of bumps.

This work has 5200 bumps, the standard deviation is 0.5 μm, and 3 δ is±1.95 μm.

If a target value is set to +/−2 μm, the work is judged good from thestandard deviation, and is transported to the next process. The work maybe judged good to transport it to the next process, if all bumps are ina range of predetermined reference values.

FIG. 16 shows examples of various displays displayed on the screen 112of the measuring apparatus.

An operation screen 300 has a display area 302 for a present operationmode and the like, an area 304 for displaying a relative heightoccurrence frequency distribution graph, an area 306 for displayingjudgement results, and an area 308 for displaying the detailed resultsfor each LSI as a work.

In the area 302, the following items are displayed.

(a) Present operation mode (alignment, apex measurement, basemeasurement, judgement calculation, second time individual measurement).

(b) Present inspection position (row, column) with graphics and values.

(c) Coordinates of defective bump of inspected LSI with graphics andvalues.

For the display of the position of a defective bump, for example, theposition of a defective bump 10-N of the work 1 is displayed withgraphics.

The relative height occurrence frequency distribution graph 304 is shownin FIG. 15. The judgement results are displayed in the area 306 by OK orNG. For the detailed results for each LSI in the area 308, the alignmentresults are displayed by values of X, Y, Z, θ, α, and β, and also a bumpaverage height, standard deviation of relative heights, received lightaverage amount, and base shrinkage ratios in X and Y directions aredisplayed.

A position shift graph screen 310 shows a distribution of a shift amountof an apex position from a design value for each bump.

A height three-dimensional distribution graph screen 320 shows a 3Dgraph of relative heights of respective bumps and a two-dimensionaldistribution graph in different colors.

A defective LSI information graph screen 330 shows a judgement mode of adefective LSI after full automatic operation (in units of magazine).

An inspection condition setting screen 340 is used for settinginspection parameters such as judgement threshold values.

With this invention, for example, an operation speed of 32 mm/sec,optical micro head frequency of 16 kHz, measurement resolution in thehorizontal direction of 2 to 3 μm, and measurement resolution in theheight direction (Z direction) of 0.05 μm, can be realized.

What is claimed is:
 1. A method of measuring solder bumps formed on awork to be measured, comprising the steps of irradiating a light beam oneach solder bump disposed on the work set on a table; measuring an apexheight of each solder bump by receiving a light reflected from eachsolder bump; determining a regression plane constituted by said solderbumps by referring to said apex heights measured; and determining arelative apex height of each solder bump relative to said determinedregression plane.
 2. A solder bump measuring method according to claim1, further comprising the steps of: judging whether a relative apexheight of each solder bump is within a predetermined value; anddisplaying positions of solder bumps judged to be of inferior quality ondisplay means.
 3. A solder bump measuring method according to claim 1,further comprising the steps of: calculating a standard deviationregarding a relative apex height of each solder bump; and judgingwhether the work is good or bad by referring to an apex height of eachsolder bump and said standard deviation.
 4. A method of measuring solderbumps formed on a work to be measured, comprising the steps of:irradiating a light beam on a surface of said work and a surface of eachsolder bump on said work set on a table; measuring a height of saidsurface of said work and an apex height of each solder bump by receivinglight reflected from said surface of said work and said surface of eachsolder bump of said work set on said table; determining a regressionplane constituted by said surface of said work from measured results;and determining a relative apex height of each solder bump relative tosaid determined regression plane.